<?php
/**
 *
 * @package diff
 * @version $Id: engine.php 8147 2007-10-05 14:36:34Z acydburn $
 * @copyright (c) 2006 phpBB Group
 * @license http://opensource.org/licenses/gpl-license.php GNU Public License
 *
 */


/**
 * Code from pear.php.net, Text_Diff-0.2.1 (beta) package
 * http://pear.php.net/package/Text_Diff/
 *
 * Modified by phpBB Group to meet our coding standards
 * and being able to integrate into phpBB
 *
 * Class used internally by Diff to actually compute the diffs.  This class is
 * implemented using native PHP code.
 *
 * The algorithm used here is mostly lifted from the perl module
 * Algorithm::Diff (version 1.06) by Ned Konz, which is available at:
 * http://www.perl.com/CPAN/authors/id/N/NE/NEDKONZ/Algorithm-Diff-1.06.zip
 *
 * More ideas are taken from:
 * http://www.ics.uci.edu/~eppstein/161/960229.html
 *
 * Some ideas (and a bit of code) are taken from analyze.c, of GNU
 * diffutils-2.7, which can be found at:
 * ftp://gnudist.gnu.org/pub/gnu/diffutils/diffutils-2.7.tar.gz
 *
 * Some ideas (subdivision by NCHUNKS > 2, and some optimizations) are from
 * Geoffrey T. Dairiki <dairiki@dairiki.org>. The original PHP version of this
 * code was written by him, and is used/adapted with his permission.
 *
 * @author  Geoffrey T. Dairiki <dairiki@dairiki.org>
 * @package diff
 *
 * @access private
 */
class diff_engine
{
  function diff(&$from_lines, &$to_lines, $preserve_cr = true)
  {
    // Remove empty lines...
    // If preserve_cr is true, we basically only change \r\n and bare \r to \n to get the same carriage returns for both files
    // If it is false, we try to only use \n once per line and ommit all empty lines to be able to get a proper data diff

    if (is_array($from_lines)) {
      $from_lines = implode("\n", $from_lines);
    }

    if (is_array($to_lines)) {
      $to_lines = implode("\n", $to_lines);
    }

    if ($preserve_cr) {
      $from_lines = explode("\n", str_replace("\r", "\n", str_replace("\r\n", "\n", $from_lines)));
      $to_lines = explode("\n", str_replace("\r", "\n", str_replace("\r\n", "\n", $to_lines)));
    } else {
      $from_lines = explode("\n", preg_replace('#[\n\r]+#', "\n", $from_lines));
      $to_lines = explode("\n", preg_replace('#[\n\r]+#', "\n", $to_lines));
    }

    $n_from = sizeof($from_lines);
    $n_to = sizeof($to_lines);

    $this->xchanged = $this->ychanged = $this->xv = $this->yv = $this->xind = $this->
      yind = array();
    unset($this->seq, $this->in_seq, $this->lcs);

    // Skip leading common lines.
    for ($skip = 0; $skip < $n_from && $skip < $n_to; $skip++) {
      if ($from_lines[$skip] !== $to_lines[$skip]) {
        break;
      }
      $this->xchanged[$skip] = $this->ychanged[$skip] = false;
    }

    // Skip trailing common lines.
    $xi = $n_from;
    $yi = $n_to;

    for ($endskip = 0; --$xi > $skip && --$yi > $skip; $endskip++) {
      if ($from_lines[$xi] !== $to_lines[$yi]) {
        break;
      }
      $this->xchanged[$xi] = $this->ychanged[$yi] = false;
    }

    // Ignore lines which do not exist in both files.
    for ($xi = $skip; $xi < $n_from - $endskip; $xi++) {
      $xhash[$from_lines[$xi]] = 1;
    }

    for ($yi = $skip; $yi < $n_to - $endskip; $yi++) {
      $line = $to_lines[$yi];

      if (($this->ychanged[$yi] = empty($xhash[$line]))) {
        continue;
      }
      $yhash[$line] = 1;
      $this->yv[] = $line;
      $this->yind[] = $yi;
    }

    for ($xi = $skip; $xi < $n_from - $endskip; $xi++) {
      $line = $from_lines[$xi];

      if (($this->xchanged[$xi] = empty($yhash[$line]))) {
        continue;
      }
      $this->xv[] = $line;
      $this->xind[] = $xi;
    }

    // Find the LCS.
    $this->_compareseq(0, sizeof($this->xv), 0, sizeof($this->yv));

    // Merge edits when possible.
    $this->_shift_boundaries($from_lines, $this->xchanged, $this->ychanged);
    $this->_shift_boundaries($to_lines, $this->ychanged, $this->xchanged);

    // Compute the edit operations.
    $edits = array();
    $xi = $yi = 0;

    while ($xi < $n_from || $yi < $n_to) {
      // Skip matching "snake".
      $copy = array();

      while ($xi < $n_from && $yi < $n_to && !$this->xchanged[$xi] && !$this->
        ychanged[$yi]) {
        $copy[] = $from_lines[$xi++];
        $yi++;
      }

      if ($copy) {
        $edits[] = &new diff_op_copy($copy);
      }

      // Find deletes & adds.
      $delete = array();
      while ($xi < $n_from && $this->xchanged[$xi]) {
        $delete[] = $from_lines[$xi++];
      }

      $add = array();
      while ($yi < $n_to && $this->ychanged[$yi]) {
        $add[] = $to_lines[$yi++];
      }

      if ($delete && $add) {
        $edits[] = &new diff_op_change($delete, $add);
      } else
        if ($delete) {
          $edits[] = &new diff_op_delete($delete);
        } else
          if ($add) {
            $edits[] = &new diff_op_add($add);
          }
    }

    return $edits;
  }

  /**
   * Divides the Largest Common Subsequence (LCS) of the sequences (XOFF,
   * XLIM) and (YOFF, YLIM) into NCHUNKS approximately equally sized segments.
   *
   * Returns (LCS, PTS).  LCS is the length of the LCS. PTS is an array of
   * NCHUNKS+1 (X, Y) indexes giving the diving points between sub
   * sequences.  The first sub-sequence is contained in (X0, X1), (Y0, Y1),
   * the second in (X1, X2), (Y1, Y2) and so on.  Note that (X0, Y0) ==
   * (XOFF, YOFF) and (X[NCHUNKS], Y[NCHUNKS]) == (XLIM, YLIM).
   *
   * This function assumes that the first lines of the specified portions of
   * the two files do not match, and likewise that the last lines do not
   * match.  The caller must trim matching lines from the beginning and end
   * of the portions it is going to specify.
   */
  function _diag($xoff, $xlim, $yoff, $ylim, $nchunks)
  {
    $flip = false;

    if ($xlim - $xoff > $ylim - $yoff) {
      // Things seems faster (I'm not sure I understand why) when the shortest sequence is in X.
      $flip = true;
      list($xoff, $xlim, $yoff, $ylim) = array($yoff, $ylim, $xoff, $xlim);
    }

    if ($flip) {
      for ($i = $ylim - 1; $i >= $yoff; $i--) {
        $ymatches[$this->xv[$i]][] = $i;
      }
    } else {
      for ($i = $ylim - 1; $i >= $yoff; $i--) {
        $ymatches[$this->yv[$i]][] = $i;
      }
    }

    $this->lcs = 0;
    $this->seq[0] = $yoff - 1;
    $this->in_seq = array();
    $ymids[0] = array();

    $numer = $xlim - $xoff + $nchunks - 1;
    $x = $xoff;

    for ($chunk = 0; $chunk < $nchunks; $chunk++) {
      if ($chunk > 0) {
        for ($i = 0; $i <= $this->lcs; $i++) {
          $ymids[$i][$chunk - 1] = $this->seq[$i];
        }
      }

      $x1 = $xoff + (int)(($numer + ($xlim - $xoff) * $chunk) / $nchunks);

      for (; $x < $x1; $x++) {
        $line = $flip ? $this->yv[$x] : $this->xv[$x];
        if (empty($ymatches[$line])) {
          continue;
        }
        $matches = $ymatches[$line];

        foreach ($matches as $y) {
          if (empty($this->in_seq[$y])) {
            $k = $this->_lcs_pos($y);
            $ymids[$k] = $ymids[$k - 1];
            break;
          }
        }

        // no reset() here
        while (list($junk, $y) = each($matches)) {
          if ($y > $this->seq[$k - 1]) {
            // Optimization: this is a common case: next match is just replacing previous match.
            $this->in_seq[$this->seq[$k]] = false;
            $this->seq[$k] = $y;
            $this->in_seq[$y] = 1;
          } else
            if (empty($this->in_seq[$y])) {
              $k = $this->_lcs_pos($y);
              $ymids[$k] = $ymids[$k - 1];
            }
        }
      }
    }

    $seps[] = $flip ? array($yoff, $xoff) : array($xoff, $yoff);
    $ymid = $ymids[$this->lcs];

    for ($n = 0; $n < $nchunks - 1; $n++) {
      $x1 = $xoff + (int)(($numer + ($xlim - $xoff) * $n) / $nchunks);
      $y1 = $ymid[$n] + 1;
      $seps[] = $flip ? array($y1, $x1) : array($x1, $y1);
    }
    $seps[] = $flip ? array($ylim, $xlim) : array($xlim, $ylim);

    return array($this->lcs, $seps);
  }

  function _lcs_pos($ypos)
  {
    $end = $this->lcs;

    if ($end == 0 || $ypos > $this->seq[$end]) {
      $this->seq[++$this->lcs] = $ypos;
      $this->in_seq[$ypos] = 1;
      return $this->lcs;
    }

    $beg = 1;
    while ($beg < $end) {
      $mid = (int)(($beg + $end) / 2);
      if ($ypos > $this->seq[$mid]) {
        $beg = $mid + 1;
      } else {
        $end = $mid;
      }
    }

    $this->in_seq[$this->seq[$end]] = false;
    $this->seq[$end] = $ypos;
    $this->in_seq[$ypos] = 1;

    return $end;
  }

  /**
   * Finds LCS of two sequences.
   *
   * The results are recorded in the vectors $this->{x,y}changed[], by
   * storing a 1 in the element for each line that is an insertion or
   * deletion (ie. is not in the LCS).
   *
   * The subsequence of file 0 is (XOFF, XLIM) and likewise for file 1.
   *
   * Note that XLIM, YLIM are exclusive bounds.  All line numbers are
   * origin-0 and discarded lines are not counted.
   */
  function _compareseq($xoff, $xlim, $yoff, $ylim)
  {
    // Slide down the bottom initial diagonal.
    while ($xoff < $xlim && $yoff < $ylim && $this->xv[$xoff] == $this->yv[$yoff]) {
      ++$xoff;
      ++$yoff;
    }

    // Slide up the top initial diagonal.
    while ($xlim > $xoff && $ylim > $yoff && $this->xv[$xlim - 1] == $this->yv[$ylim -
      1]) {
      --$xlim;
      --$ylim;
    }

    if ($xoff == $xlim || $yoff == $ylim) {
      $lcs = 0;
    } else {
      // This is ad hoc but seems to work well.
      // $nchunks = sqrt(min($xlim - $xoff, $ylim - $yoff) / 2.5);
      // $nchunks = max(2,min(8,(int)$nchunks));
      $nchunks = min(7, $xlim - $xoff, $ylim - $yoff) + 1;
      list($lcs, $seps) = $this->_diag($xoff, $xlim, $yoff, $ylim, $nchunks);
    }

    if ($lcs == 0) {
      // X and Y sequences have no common subsequence: mark all changed.
      while ($yoff < $ylim) {
        $this->ychanged[$this->yind[$yoff++]] = 1;
      }

      while ($xoff < $xlim) {
        $this->xchanged[$this->xind[$xoff++]] = 1;
      }
    } else {
      // Use the partitions to split this problem into subproblems.
      reset($seps);
      $pt1 = $seps[0];

      while ($pt2 = next($seps)) {
        $this->_compareseq($pt1[0], $pt2[0], $pt1[1], $pt2[1]);
        $pt1 = $pt2;
      }
    }
  }

  /**
   * Adjusts inserts/deletes of identical lines to join changes as much as possible.
   *
   * We do something when a run of changed lines include a line at one end
   * and has an excluded, identical line at the other.  We are free to
   * choose which identical line is included. 'compareseq' usually chooses
   * the one at the beginning, but usually it is cleaner to consider the
   * following identical line to be the "change".
   *
   * This is extracted verbatim from analyze.c (GNU diffutils-2.7).
   */
  function _shift_boundaries($lines, &$changed, $other_changed)
  {
    $i = 0;
    $j = 0;

    $len = sizeof($lines);
    $other_len = sizeof($other_changed);

    while (1) {
      // Scan forward to find the beginning of another run of
      // changes. Also keep track of the corresponding point in the other file.
      //
      // Throughout this code, $i and $j are adjusted together so that
      // the first $i elements of $changed and the first $j elements of
      // $other_changed both contain the same number of zeros (unchanged lines).
      //
      // Furthermore, $j is always kept so that $j == $other_len or $other_changed[$j] == false.
      while ($j < $other_len && $other_changed[$j]) {
        $j++;
      }

      while ($i < $len && !$changed[$i]) {
        $i++;
        $j++;

        while ($j < $other_len && $other_changed[$j]) {
          $j++;
        }
      }

      if ($i == $len) {
        break;
      }

      $start = $i;

      // Find the end of this run of changes.
      while (++$i < $len && $changed[$i]) {
        continue;
      }

      do {
        // Record the length of this run of changes, so that we can later determine whether the run has grown.
        $runlength = $i - $start;

        // Move the changed region back, so long as the previous unchanged line matches the last changed one.
        // This merges with previous changed regions.
        while ($start > 0 && $lines[$start - 1] == $lines[$i - 1]) {
          $changed[--$start] = 1;
          $changed[--$i] = false;

          while ($start > 0 && $changed[$start - 1]) {
            $start--;
          }

          while ($other_changed[--$j]) {
            continue;
          }
        }

        // Set CORRESPONDING to the end of the changed run, at the last point where it corresponds to a changed run in the
        // other file. CORRESPONDING == LEN means no such point has been found.
        $corresponding = $j < $other_len ? $i : $len;

        // Move the changed region forward, so long as the first changed line matches the following unchanged one.
        // This merges with following changed regions.
        // Do this second, so that if there are no merges, the changed region is moved forward as far as possible.
        while ($i < $len && $lines[$start] == $lines[$i]) {
          $changed[$start++] = false;
          $changed[$i++] = 1;

          while ($i < $len && $changed[$i]) {
            $i++;
          }

          $j++;
          if ($j < $other_len && $other_changed[$j]) {
            $corresponding = $i;
            while ($j < $other_len && $other_changed[$j]) {
              $j++;
            }
          }
        }
      } while ($runlength != $i - $start);

      // If possible, move the fully-merged run of changes back to a corresponding run in the other file.
      while ($corresponding < $i) {
        $changed[--$start] = 1;
        $changed[--$i] = 0;

        while ($other_changed[--$j]) {
          continue;
        }
      }
    }
  }
}

?>